Hi Kuki, the real answer depends on what you are comparing Cunard against, which level of stateroom you would book as it is still a 2-tier class liner, and which of the Cunard fleet you are looking at.

The builds of QE & QV are the same only with different decor, and follow an "out of the box" industry standard design for large cruise ships, whilst QM2 is completely different.

As Henry43 said, they still have the white glove afternoon tea service, which unlike some lines (Fred.Olsen) is included in the price of your voyage.
To us, the QM2 feels more formal than her younger sisters, but that may be because she spends so much time running the TransAtlantic route, so has different objectives. For us QV (and hopefully QE) are far more in line with other 'British' brands, where formality is still required, but the entertainment & venues on board feel more relaxed.

If you let us know what aspects you are wanting to compare, and which liner you are thinking of trying. Then we will try to offer a more precise reply.

Kuki, I would echo the previous poster's comments. What aspect of Cunard are you interested in because the QM2 does vary slightly from her smaller sisters the new QE and the QV.
On the QM2 except for embarkation day afternoon tea is served by white-gloved waiters in the ballroom and it's very popular. She has the only Planetarium at sea and all 3 ships have excellent libraries.
Are you interested in a transatlantic or a cruise-type voyage? That would dictate which ship you choose since the QV and QE do only a few crossings per year.
Linda

My wife and I are both "over 50" and we like the elegance and more formal aspect of Cunard. In particular, we love the QM2. On our honeymoon in 1983 we went on a Holland Amercian ship and enjoyed that, but have been Cunard exclusively since then. Except for this last summer when friends wanted to go on a Norwegian Cruise Line ship for a Baltic Cruise. Overall, I enjoyed it, but it didn't come anywhere close to the QM2 with respect to what I look for in a cruise.

My wife and I don't dislike children, but we prefer there to be very few of them on the ship when we cruise. We took the QM2 transatlantic during the summer of 2009. I recall hearing a young teenager at a next table say "This ship has the worst teen club I've ever been to." For me, that was a ringing endorsement of the QM2.

We did one short cruise on QE2 we thought everything was just "classy" we have yet to try QM2 but a P&O officer friend who was seconded to Cunard(they swop about) says QM2 is a fine ship..it's the class thing that concerns me.

We did one short cruise on QE2 we thought everything was just "classy" we have yet to try QM2 but a P&O officer friend who was seconded to Cunard(they swop about) says QM2 is a fine ship..it's the class thing that concerns me.

There is and there isn't a class system.
Queens and Princess Grills have their own dining rooms and a lounge. There is also a small area of deck reserved for them (QM2). Otherwise they share everything else. In the theater, on a shore excursion, at a lecture, etc. you wouldn't know who has what grade of cabin.
The grills are also a small minority, since the majority of cabins are Britannia grade.
Linda

As far as I am concerned if there are places I cannot go because of the grade of cabin I am in that is a class system. Not saying it's good or bad just I feel uncomfortable with it, I suppose if famous people want a bit of privacy it's the only way.

It's never really bothered me. I personally think the Britannia dining room is much nicer than the Grill dining rooms. Those dining rooms and their lounge are at the rear of deck 7 and I seldom think about them.

Just because you choose to spend that amount of money for a Grill cabin doesn't make you any better or famous than the masses. One evening I went up to the Grill dining room to see a maitre d' friend of mine and observed the diners coming and going and frankly I was much better dressed than some of them.

So by now you have probably tried Cunard. How did it go? If not , then just be aware of hte formal atmosphere. If like to dress up, then go Cunard. I love it. People there are NOT snobs. You can be just as friendly in a tux as in shorts and t-shirt. But if you have dressed up for a formal dinner or a ball and someone wants to come in in jeans and t-shirt... it just doesn't add to the atmosphere. Sorry if that offends.